Image-Based Reduction of Artifacts in Multishot Echo-Planar Imaging

The method to reduce the ghost artifact in echo-planar imaging (EPI) using a phase correction derived from the image data (M. H. Buonocore and L. Gao,Magn. Reson. Med.38, 89 (1997)) is generalized to multishot (interleaved) EPI, where the artifact takes the form of multiple ghosts. The method is shown to be much more sensitive to noise when applied to standard interleaved data than is the case with single-shot EPI, because the calculation must be based on high-order ghosts of low intensity. A modified interleaving scheme is proposed for multishot EPI in which the initial trajectory direction alternates in consecutive shots and the number of shots is odd. With this scheme, only a single ghost shifted by one-half of the field of view appears just as in the single-shot EPI, and the image-based phase correction can be applied with the usual sensitivity to noise.     

On extending backwards positive definite sequences

The two-sided Hamburger moment problem¹, also called the strong one [4], has been extensively studied in recent years in connection with rational approximation. We propose to consider the question of when a sequence, say {a _n } _n=0 can be extended backwards so that the resulting sequence {a _n } _n=–N has an integral representation of the Hamburger type. This was settled (without any proof) under different circumstances in [6]. Here we wish to discuss this completely, as well as the possibility of extending {a _n } _n=0 to {a _n } _n– .     

Photometrische Bestimmung von Perchlorat mit Ferroin

Zusammenfassung Ein Verfahren zur photometrischen Bestimmung des Perchlorations wurde ausgearbeitet. Die Untersuchungslösung wird mit überschüssigem Ferroin und mit Chloroform versetzt. Der Niederschlag wird, abfiltriert und der Ferroinüberschuß im Filtrat photometrisch bestimmt. Für die Bestimmung kleiner Perchloratmengen zwischen 0,2 und 1 mg extrahiert man den gefärbten Ferroinperchloratkomplex mit n-Amylalkohol und photometriert die alkoholische Phase. Der Einfluß von Fremdionen auf die Analysenergebnisse wurde untersucht.

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Summary A method was worked out for the photometric determination of perchlorate ion. The test solution is treated with excess ferroin and chloroform. The precipitate is filtered off and the excess ferroin in the filtrate is determined photometrically. When slight amounts of perchlorate are to be determined, say between 0.2 and 1 mg, the colored ferroin-perchlorate complex is extracted withn-amyl alcohol and the alcoholic phase is photometerized. The effect of foreign ions on the analytical findings was studied.

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Résumé On a mis au point un procédé pour le dosage photométrique de l'ion perchlorate. On additionne la solution à l'étude de ferroine et de chloroforme. en excès. Le précipité est séparé par filtration et l'excès de ferroine dosé photométriquement sur le filtrat. Pour le dosage de petites quantités de perchlorate, entre 0,2 et 1 mg, on extrait le complexe coloré perchlorate de ferroine par l'alcooln-amylique et l'on effectue la photométrie sur la phase alcoolique. On a étudié l'influence des ions étrangers sur les résultats d'analyse.

     

Comparison of Flow and Transport Experiments on 3D Printed Micromodels with Direct Numerical Simulations

Understanding pore-scale flow and transport processes is important for understanding flow and transport within rocks on a larger scale. Flow experiments on small-scale micromodels can be used to experimentally investigate pore-scale flow. Current manufacturing methods of micromodels are costly and time consuming. 3D printing is an alternative method for the production of micromodels. We have been able to visualise small-scale, single-phase flow and transport processes within a 3D printed micromodel using a custom-built visualisation cell. Results have been compared with the same experiments run on a micromodel with the same geometry made from polymethyl methacrylate (PMMA, also known as Perspex). Numerical simulations of the experiments indicate that differences in experimental results between the 3D printed micromodel and the Perspex micromodel may be due to variability in print geometry and surface properties between the samples. 3D printing technology looks promising as a micromodel manufacturing method; however, further work is needed to improve the accuracy and quality of 3D printed models in terms of geometry and surface roughness.

     

Selfadjointness of Integral and Matrix Operators

Criteria for selfadjointness of integral operators, includingmatrix operators, based on our earlier domination results areestablished. The range of applicability is elucidated by carefullychosen examples, not covered by previously known criteria.     

Resolution of indobufen enantiomers by capillary zone electrophoresis. Pharmacokinetic studies of human serum

A direct and stereospecific method was worked out to quantify indobufen enantiomers in human serum using capillary zone electrophoresis (CZE). The indobufen enantiomers and (+)-S-ketoprofen (internal standard, IS) were separated in a fused silica capillary, filled with heptakis 2,3,6-tri-O-methyl-beta-cyclodextrin as a chiral selector in a buffer of pH 5.0. Indobufen enantiomers and other non-steroidal anti-inflammatory drugs: flurbiprofen, ketoprofen and (+)-S-naproxen were also separated during one analytical run. UV absorbances of indobufen enantiomers were measured at 282 nm. Influence of temperature on resolution of the enantiomers, and the electrophoretic parameters: electrophoretic (muep) and electroosmotic (muEOF) mobilities were also determined. Validation of the method was carried out. Calibration curves of indobufen enantiomers were linear in the range of 0.2-20.0 microg/ml. Percent recovery of both enantiomers from acidified serum was calculated after extraction with methylene chloride. Intra- and inter-day measurement precision and accuracy were below 15.0%. Limits of quantitation and detection were also estimated. The elaborated method was tested in vivo after administration of a single dose of 200 mg rac-indobufen tablets to healthy volunteers. Calculated parameters confirmed usefulness of the method in human pharmacokinetic studies on indobufen enantiomers. The direct CZE method can provide an alternative to HPLC, where enantiomers used to be derivatised before determination.     

Charlier Polynomials and Translational Invariance in the Quantum Harmonic Oscillator

In a recent paper [5] the creation operator of the quantum harmonic oscillator (its counterpart, the annihilation one as well) is characterized through its (spatial) translational invariance property. Here we step up with replacing the operator theoretic reasoning of [5] by an orthogonal polynomial environment which let the arguments become natural. This settles the result well in the circumstances of [8] (as well as those of [7]).     

Data-driven curvilinear reconstructions of 3D MR images: application to cryptogenic extratemporal epilepsy

This paper presents a data-driven method for the reconstruction and visualisation of curvilinear slices from three-dimensional (3D) magnetic resonance (MR) scans of the head. Visualisation of curvilinear slices, rather than standard planar slices, produces symmetrical views of the cortex and allows small abnormalities to be detected by comparing the two hemispheres of the brain. In our method, the surface defined by the upper half of the brain is used as a reference shape for curvilinear reconstructions. The brain is first segmented from the 3D scan using a 3D region growing method associated to an unsupervised threshold selection technique. The upper half of the segmented brain is then extracted and fitted by a deformable surface model. This surface is finally interactively moved by the operator in the 3D scan, to visualise the desired curvilinear slice, which is projected on the screen as a two-dimensional image. We show an application of this visualisation technique to the localisation of cerebral epileptogenic lesions. The procedure has proven efficient and handy in clinical use.